We are attempting to characterize the active alkali metal ion transport system of the isolated silkworm midgut. Presently we are devoting most of our efforts to the kinetic analysis of the system. Preliminary work is underway to isolate the chemical components. The project is viewed as a model for transepithelial ion transport including transport in vectors and as a prospective tool in the control of plant eating insects. We have lingered with the kinetic analysis because we are finding that our steady-state analysis of the kinetics forces us to develope new techniques and concepts, and yields results which are inconsistent with older work on the midgut and other epithelial systems. Specifically we have measured the size of the transport pool and have determined its location as well as the location of the active K-transport system. We are now studying the ion-competition for the K-pump, looking for specific inhibitions of it and attempting to isolate its components.